Have a 2002 Dodge Ram 1500 with a 5.9. Have had it for a couple of months without issue. Alternator was working fine but had a loud whine to it because of the bearings. Previous owner said it was like that for years. I didn't like the noise so I replaced the alternator with one from Autozone. After driving it for 5 to 10 minutes the voltage gauge drops to the far left and the check gauges light comes on. Autozone tested the Alternator and said it's only putting out 12v. I got another one from them and had the same problem. I put the old one back in and had the same problem. Must be something new that happened when switching the alternator out. Any ideas? Battery test is good.